The invention relates to a intake pipe for an internal combustion engine comprising at least two shells that are welded together. Intake pipes of the aforementioned type are known, for example, from EP 568,560. According to FIG. 15 of this document, the depicted intake pipe is made of two shells, which form the intake channels of the intake pipe. The joining surfaces for welding the shells together are provided within welding edges 425, 426. They form a joint line 420, which in the depicted example is identical with the joining surfaces.
The figure also shows the direction of force applied by the welding tool. The joint line 420 is configured in such a way that the angle of inclination of the joint line does not substantially exceed a 60xc2x0 angle relative to a plane that is perpendicular to the welding force. This is to achieve a reliable weld joint along the entire joining surface. The inclination of the joint line relative to the applied welding force may therefore not be substantially less than 30xc2x0.
The configuration of the joint line protected by EP 568,560 ensures the functioning of the intake pipe to the extent that the intake pipe can withstand the pressure conditions that occur within the intake pipe. However, the depicted configuration limits the freedom of design regarding the geometry of the intake pipe. The curved intake channels can be produced with two shells only up to a certain angle of curvature. A larger angle of curvature of the joint line can no longer be adequately adapted to the curvature of the intake channel, and undercuts would be created as a result.
It is an object of the invention to provide an improved intake pipe for an internal combustion engine comprised of at least two shells which are welded together.
Another object of the invention is to provide an intake pipe for an internal combustion engine comprised of at least two shells welded together which achieves increased design flexibility while at the same time assuring durability and reliability of the welds which join the shells.
A further object of the invention is to provide a intake pipe whose shells can be optimally adapted to the required geometric conditions of the housing.
These and other objects have been achieved in accordance with the present invention by providing an intake pipe for an internal combustion engine, the intake pipe comprising a housing having an inlet and at least one cylinder outlet for combustion air and including a plenum from which at least one intake channel branches off to the respective outlet for each cylinder of the internal combustion engine, wherein the housing is formed by at least two shells that are welded together at mating joining surfaces which define a joint line between the shells, the joint line having sections with differing inclinations relative to the direction of a joining force applied by a welding tool, and wherein, at least in a section of the joint line that has the smallest inclination relative to the direction of the joining force, the inclination of the joining surfaces alternately has a greater inclination than the joint line and then a smaller inclination than the joint line.
The intake pipe according to the invention comprises two shells that are welded together. Suitable welding processes for welding the shells include, e.g., vibration welding and/or ultrasonic welding. For the welding procedure, the intake pipe is inserted into suitable welding tools that will adequately support the intake pipe shells. These welding tools also apply a welding force to the parts to be joined.
To facilitate connection of the shells of the intake pipe to each other, the shells are provided with joining surfaces. These joining surfaces define a joint line, which has sections of different inclinations relative to the direction of the joining force. They can be adjacent linear sections without curvature. Generally, however, the joint line will be continuously curved. This is particularly advantageous if the shells together form curved intake channels of the intake pipe and their curvature follows the curvature of the intake channels at least in sections. The joint line results from the average inclination of the joining surfaces in the individual sections. In other words, the joint line deviates from the joining surfaces in sections that comprise an abrupt change in the inclination of the joining surfaces. In continuous sections of the joining surfaces, the joining surfaces are largely identical with the joint line.
The intake pipe according to the invention is characterized in that, at least in a section of the joint line where the joint line has the smallest inclination relative to the direction of the joining force, the inclination of the joining surfaces alternately adopts a greater and then a smaller inclination. This alternation between greater and smaller inclination can occur once or several times within this section.
The section of the joint line with the smallest inclination is the one where the attainable strength values of the weld seam must be viewed as the most critical. The configuration of the joining surfaces according to the invention is a way to assure that adequate strength of the weld seam is also achieved in these areas. This is achieved by the fact that the areas with a greater inclination relative to the joining force result in more favorable strength values of the weld seam than would be possible with joining surfaces that are identical with the joint line. In these areas, the joint line has a smaller inclination relative to the direction of the welding force, which would result in more critical values. Due to the adequate strength of the weld seam in the area of the joining surfaces that have a greater angle of inclination than the joint line, it is possible to accept the reduced strength of the sections of the joining surfaces whose angle of inclination relative to the welding force is smaller than that of the joint line. These weaker areas are relieved by the strong sections with respect to compression loads and must merely satisfy a sealing function.
The described configuration of the joining surfaces allows greater geometric freedom in the design of the shells of the intake pipe. It is possible, in particular, to obtain joint lines whose inclination relative to the joining force can also be substantially smaller than 30xc2x0. In particular, even angles of less than  less than 24xc2x0 can be achieved. Relative to a plane that is perpendicular to the welding force, maximum angles of inclination of the joint line of substantially more than 60xc2x0, especially more than 66xc2x0, are created.
One specific embodiment of the invention is obtained if in a projection, the joint line has a constant curvature. This projection results from the viewing direction onto the joint line from a certain perspective. If the joint line extends, for example, along the curvature of the intake channels of the intake pipe, the described projection results, for instance, if the viewing direction onto the intake channels is perpendicular to the curvature. Thus, the welding force is perpendicular to this viewing direction. The welding force is directed in such a way that at the end of the projection, which coincides with the end of the joint line, there is a section of the joint line, at least on one side, where the inclination relative to this force is smallest. In this area, the above-described stepped course of the joining surfaces around the joint line is provided. In this configuration of the joining surfaces, this results in sections in the center area of the joint line whose inclination relative to the joining force is non-critical, so that in these areas the joint line can be identical with the joining surfaces.
An especially advantageous embodiment of the invention is obtained if the areas of the joining surfaces having a smaller inclination than the joint line are at least approximately perpendicular to the direction of the joining force. If the joining surfaces are perpendicular to the joining force, the resulting strength of the weld seam is optimal. These areas can then absorb the loads occurring along the weld seam particularly well. As a result the sections of the joining surfaces with the strongest inclination, which alternate with those of a smaller inclination, can adopt angles of inclination of less than 24xc2x0 relative to the joining force.
Another specific embodiment of the joining surfaces in the area where their course deviates from that of the joint line, is a stepped configuration. The steps can have rounded corners to achieve an optimum welding result even in the area of the change in inclination. The stepped course provides optimal protection against failure of the areas with the smaller inclination relative to the joining force.
According to another variant, a weld rim can hide the change in the inclination of the joining surfaces. This improves the visual appearance of the intake pipe.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either alone or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.